Variable resistor with foil parts



Oct. 13, 1970 P, TRONCA ET AL 3,534,316

VARIABLE RESISTOR WITH FOIL PARTS Filed Jan. 5, 1967 2 Sheets-Sheet 2 I NVENTORS DENNIS TRO/VCA JOHN/1! HAGEDORN PE/VDLE TON, NEUMA/V SE/BOLD 8 W/LL/AMS ATTORNEYS United States Patent 3,534,316 VARIABLE RESISTOR WITH FOIL PARTS Dennis Pat Tronca, Thiensville, and John Harley Hagedorn, Milwaukee, Wis., assignors to Globe-Union Inc.,

Milwaukee, Wis., a corporation of Delaware Filed Jan. 5, 1967, Ser. No. 607,531

Int. Cl. H01c /02 U.S. Cl. 338174 Claims ABSTRACT OF THE DISCLOSURE A rotary variable resistor having a metallic foil center take-off adhesively secured to a base portion for reducing the material and production costs of the device.

Variable resistors or potentiometers are used extensively in electrical circuits to enable manual adjustment of electrical resistance. A typical construction is a rotary variable resistor-including a circular arc of resistive material, having its two ends terminated for connection in an electric circuit, and a manually rotatable wiper arm contacting both the resistive arc and a center take-off through which the wiper arm is connected to the external circuit. As the wiper arm is rotated, the position at which it contacts the resistive are changes with the result that the resistance value varies between the wiper arm and the terminated ends of the arc.

Many applications of variable resistors require relatively low cost construction. One of the major elements of expense has been the take-01f which provides the electrical connection between the wiper arm and the external circuit. The typical prior art construction of the takeoff is a piece of stamped metal secured to the same base as the resistive material. A number of alternatives to the stamped metal part have been proposed in the interests of the cost reduction but none have proven entirely satisfactory.

It is therefore an object of the present invention to provide a novel variable resistor or potentiometer.

It is a further object of the present invention to provide a novel, low cost, variable resistor.

It is a further object of the present invention to provide a novel take-off for a variable resistor.

Briefly, the above objects are accomplished in part by forming a take-off for a variable resistor from a conductive foil, preferably a silver-copper alloy. The foil is secured to an insulating base member such as a paper base laminate by a suitable adhesive. The resistive material, which may be a resistive paint, is also positioned on the base and a wiper arm or contactor provides an electrical connection between the center take-ofr and the resistive arc.

The low cost of the resistor is due both to the relatively low cost of the metal foil take-0E and to the ease with which the resistor may be manufactured in large quantities. The fabrication of the take-off portion is accomplished, according to the present invention, by simply punching out the take-off parts from a strip of adhesively backed metallic foil and immediately transferring the punched parts to the base of the resistor.

The invention will be described in further detail in connection with the accompanying drawings in which:

FIG. 1 is an isometric exploded view of one embodiment of a variable resistor constructed according to the present invention.

FIG. 2 is a bottom view of part of the variable resistor shown in FIG. 1.

FIG. 3 is a front view, partially in section, of a die used to construct the center take-01f portion of this variable resistor.

FIG. 4 is a side view of the die shown in FIG. 3.

FIlfIG. 5 is a plan view of a portion of the die shown in FIG. 6 is a sectional view of a portion of the die shown in FIG. 3.

The variable resistor shown in FIG. 1 includes a thin nonconducting base 10, an arc of resistive material 11 on the base 10, and two low resistance conductive terminations 12 at the two ends of the resistive arc 11. The nonconducting base 10 is preferably a commercial paper base laminate, the resistive are 11 may be any type of conventional resistive material such as sprayed carbon composition paint, and the terminations 12 may be conventional silver paint. The resistive are 11 partially surrounds a center take-off 13 formed of a thin metallic foil adhesively secured to the base portion 10. The foil is preferably a silver-copper alloy, such as full hard Consil alloy available from Handy and Harman, and is approximately .001 inch thick. Any suitable adhesive may be used to secure the foil 13 to the base 10. For example, an X-1l40 cement available from Minnesota Mining and Manufacturing Company may be used. The center take-off 13 includes a circular portion 14, concentric with the are 11, and a stem portion 15 connecting the circular portion 14 with the edge of the device. The stem 15 provides means for electrically connecting the center talked-off to the external circuit in which the device is use Just below the circular portion 14, the edges of the stem 15 are slightly depressed into two recesses 16 formed in the base 10 and a crown 17 is formed in the region between the two edges. The crown 17 is also somewhat depressed below the surface of the base 10.

A hole 18 is formed in both the circular portion 14 and the base 10 at the center of the device. The hole 18 is for assembly purposes.

A metallic bridging contactor or wiper arm 20 is shown above the base portion 10. When the potentiometer is assembled the contactor 20 forms the variable electrical connection between the center take-off 13 and the resistive are 11. Two indents 21, 22 are provided on two arcuate members 23, 24 to contact, respectively, the center take-off 13 and the resistive arc 11. The contactor 20 is bent slightly along the portion 25 joining the two arcuate members 23, 24 to ensure a pressure contact between the indents 21, 22 and the circular portion 14 of the center take-01f 13 and the resistive element 11.

A rotatable plastic cover 30 covers both the contactor 20 and the base 10 when the resistor is assembled. A bottom view of the cover 30 is shown in FIG. 2. The cover 30 includes a disc 31, a post 32 extending from the disc 31, an annular projection 33 formed with two slots 34, and a stop member 35. The post 32 fits into the hole 18 enabling the cover 30 to rotate therein. A flared portion 36, shown for purposes of illustration in FIG. 2, is formed after the post 32 is inserted in the hole 18 to provide a mechanical connection. The flaring may easily be accomplished by merely heating the peripheral portion of the bottom of the post 32 under pressure. A screwdriver slot 37 is provided in the bottom of the post 32 to enable adjustment from the bottom of the resistor.

In the assembled resistor, the contactor 20 is held by the annular projection 33 of the cover 30. The smaller arcuate section 23 of the contactor 20- fits between the post 32 and the annular projection 33 while the larger arcuate section is positioned on the other side of the projection 33. The indents 21, 22 extend beyond the edge 38 of the annular projection 33 for contact with the center take-off portion 13 and resistive are 11. The two connecting portions 25 rest in the slots 34 formed in the annular projection 33 so the contactor rotates with the cover 31.

In the assembled resistor, rotation of the cover 30 varies the position of the contactor 20 to vary the resistance between the center take-off portion 13 and the two conducting leads 12. The annular projection 33 contacts the base portion to prevent tilting and the crown 17 of the center take-off 13 prevents the projection 33 from tearing the foil. An indicator 39 is provided on the cover member 30 as is a second screwdriver slot 37. The stop member 35 cooperates with the edge portions 40 of the base 10 to limit the extent of rotation of the cover 30.

The variable resistor of the present invention is easily manufactured at relatively low cost, primarily because the center take-off 13 is a low cost part and enables a relatively simple construction operation. One method for producing resistors in large quantities will be described in connection with the remaining figures of the drawings which illustrate a die used in the construction process. Briefly, the method involves the following steps: (1) a plurality of resistive arcs 11 terminating in conductive ends 12 are formed at adjacent portions of a strip of laminate; (2) the laminate strip is passed through a die, described below, which punches the center take-off portion 13 from a strip of adhesively backed metal foil; (3) the die transfers the foil to the laminate to form an adhesive bond; (4) with the foil attached, each of the individual base portions 10 is punched from the laminate, a hole 18 is formed at the center of the base and the crown 17 is formed on the stem (5) the cover 30 with the attached contactor is secured to each base 10 by flaring the post 32 as described above.

Referring to the front and side sectional views of FIGS. 3 and 4, the die which performs the punching and transferring step includes basically two sections. The upper section includes a top portion 50 with two guide pins 51, 52 and a blanking member 53 secured thereto by a plate 54 positioned just below the top portion 50 and secured thereto by suitable fasteners 55. The blanking member 53 is spring mounted in the top portion by a spring 56.

The bottom portion of the die includes a base 60 having two guide holes 61, 62 for receiving the guide pins 51, 52 from the upper portion of the die. Positioned just above the base is a first pair of guide plates 63 having a slot 66 cut therein to receive a strip of laminate base material 70. As best seen in the top view of the bottom portion of the die of FIG. 5, a second pair of guide plates 67 is positioned just above the first pair 63 and slots 73 are cut therein to receive a strip of metallic foil 75 from which the center take-off portions are cut. Between both pairs 63, 67 of guide plates and near the center of the die, are positioned four plates 76 forming a bore 77 in the shape of the center take-off portion. The bore 77 receives the blanking member 53 from the upper portion of the die. Suitable fasteners 78 are used to secure the various plates to the base 60.

Pivotally mounted on each of the second guide plates 67 is an indexing mechanism, best shown in FIG. 6. The mechanism includes a lever 80 which is pivotally mounted about a screw 81 attached to the second guide plate 67. One end of the lever is attached to a small plunger 82 which fits into an indexing hole 83 in the laminate strip 70. The other end 84 of the lever 80 contacts two springs, one 85 attached to the upper portion of the die and the other 86 attached to the lower portion of the die.

In the operation of the die, a laminate strip 70, which has deposited thereon a plurality of arcuate resistive portions 11 and terminating conductive portions 12, is fed into the die as indicated in FIG. 5. Also, a strip of adhesively backed metallic foil 75 is fed into the die between the two pairs 63, 67 of guide plates. With both the laminate and adhesive backed metallic strips positioned in the die, the upper portion is depressed by suitable means (not shown) and the blanking member 53 cuts out from the metallic foil 75 a center take-off portion and transfers it to the laminate strip 70. The transfer is accomplished with sufficient pressure to provide an adhesive bond between the foil 75 and the laminate material 70. With the die in this depressed condition the spring on the upper portion of the die (FIG. 6) exerts sufficient pressure on the lever 80 to remove the plunger 82 on the other end of the lever 80 from the index hole 83 in the laminate 70. On the other hand, the guide pins 51, 52 of the upper portion of the die pass through indexing holes 90 in the laminate strip. As the die is returned to its uppermost position and the guide pins 51, 52 are removed from the laminate, the pins 82. on the end of the two levers 80 tend to return to their positions in the indexing holes of the laminate. However, if the lami nate is advanced slightly before the pins 82 return to the indexing holes then the pins 82 will rest on top of the laminate 70 until the laminate 70 is advanced to the next hole. At that time the pins 82 will insert themselves in the holes locking the laminate for the next depression of the plunger.

It should be noted that while the die for punching and transferring the foil has been described in some detail, many other techniques may be used and will be evident to one skilled in the art. Furthermore, while one embodiment of a variable resistor constructed according to the present invention has been described in detail, the invention is not intended to be limited thereto. The following claims are intended to embrace all modifications and equivalents of the invention.

What is claimed is:

1. A variable resistor comprising a nonconducting base member, a resistant path on said base :member, said path partially surrounding a center portion and having two terminated ends, a terminated piece of conductive foil posi tioned in said center portion, and adhesively secured thereto, and movable means providing electrical connection between said foil and said resistant path.

2. The variable resistor of claim 1 wherein said conductive foil is a silver-copper alloy.

3. The variable resistor of claim 1 wherein said foil is approximately .001 inch thick.

4. The variable resistor of claim 1 further includingv a cover portion rotatably secured to said base portion and attached to said movable means, whereby the movable means is rotated when the cover is rotated.

5. The variable resistor of claim 4 wherein said cover portion includes an annular projection having an edge engaging the base and a portion of the foil, said portion of the foil being depressed below the remainder of the foil.

6. A variable resistor comprising a nonconducting base member, a resistant path on said base member, said path partially surrounding a center portion and having two terminated ends, a terminated piece of conductive foil positioned in said center portion, movable means providing electrical connection between said foil and said resistant path, a cover portion rotatably secured to said base portion and attached to said movable means, whereby the movable means is rotated when the cover is rotated, said cover including an annular projection having an edge engaging the base and a portion of the foil, the edges of said portion of the foil being depressed below the remainder of the foil, said movable means comprising two arcuate portions with two raised portions respectively formed in the arcuate portions, said movable means being positioned in slots formed in said annular projection with one of said arcuate portions in the interior of said annular projection and the other of said arcuate portions on the exterior of said annular projection with said raised portions extending beyond the annular projection.

7. The variable resistor of claim 6 wherein one of said raised portions contacts said resistant path and the other contacts said foil.

8. A variable resistor comprising, in combination:

(a) a base member;

(b) a resistive path on said base member having ter' minal means at opposite extremities;

(c) a terminated conductive foil adhesively secured to said base member adjacent said resistive path; and

((1) means movable relative to and simultaneously contacting a portion of said resistive path and said foil for providing an electrical connection therebetween.

9. A variable resistor comprising a nonconducting base member, a resistant path on said base member, said path partially surrounding a center portion and having two ends, a silver-copper alloy foil approximately .001 inch thick adhesively secured to base member in said center portion, means for providing electrical connection to said two ends and to said foil, and movable means providing electrical connection between said foil member and said resistant material.

10. A variable resistor comprising a nonconducting base member, a resistant path on said base member, said path partially surrounding a center portion and having two terminated ends, a terminated piece of conductive foil positioned in said center portion, a cover portion rotatably secured to said base portion, including an annular projection having an edge engaging the base, a por-' tion of said foil being depressed into said base in the vicinity of said annular projection, and movable means attached to said cover for providing electrical connection between said foil and said resistant path.

References Cited UNITED STATES PATENTS 2,866,876 12/1958 Cohen 338-174 3,096,499 7/1963 Hudson et a1 338-174 X ROBERT K. SCHAEFER, Primary Examiner J. HOHAUS-ER, Assistant Examiner 

